In the course of manufacture of certain electrical devices, it is often necessary to apply solder to parts of the device that are coated with a thermo-plastic insulation. These parts may be soldered by a manually controlled dip solder method, wherein a device, or a group of devices, is loaded in a fixture which is moved to dip the parts in a pot of molten solder. The part is held in the solder pot for a time sufficient to melt the insulation, whereafter solder is deposited on the now insulation free immersed portions of the part. Insulation removal and solder deposit at acceptable manufacturing rates is attained by heating the solder well above the solder melting point, e.g., 700.degree. F., and then holding the parts in the solder pot for a period of time, e.g., three seconds. However, this method is still slow and the temperature encountered often results in heat damage to other portions of the electrical device.
More specifically, the use of high temperature soldering methods may induce thermo-stress or shock. For example, where the parts to be soldered are terminal posts extending from a coil frame with the ends of the insulation coated coil wires wrapped around the square terminal posts, the heat encountered in the dip process may expand the wires which are subsequently contracted during cooling to strain the wire at the junction of the wire wrappings and the square edges of the terminal posts. Such stressing at the junction may lead to breakage of the wires. In addition, the high heat may result in the melting of the insulation on the coil wires resulting in shorting out certain of the coils thus ruining the device. Further, with the use of the solder dip method, the melted insulation abets the formation and build-up of dross and other impurities on the surface of the solder pot, thus requiring frequent dross skimming operations.
What is needed is a continuous process wherein the parts may be rapidly loaded into fixtures which are transported to move the parts through a wave solder machine to remove the insulation and solder the parts, whereafter the soldered parts may be rapidly ejected from the fixtures. Numerous wave solder machines are available for applying solder to non-coated metal parts. As an example, U.S. Pat. No. 3,482,755 to J. A. Raciti, issued Dec. 9, 1969, shows a machine for producing a solder wave which crests and falls away in opposite directions. A first portion of the solder wave falls back into a solder reservoir, while the second portion is flowed along a path that is in the direction of movement of terminals projecting from the underside of a conveyor moved circuit board. The solder path along which the terminals are advanced is configured to impart turbulence to the solder stream that acts to inhibit the formation of solder icicles projecting from the terminals and solder bridges extending between adjacent terminals.